(1) Field of the Invention
The present invention relates to a device for folding a blade, to a blade fitted with the device, and to an aircraft.
(2) Description of Related Art
An aircraft may have a rotor provided with a plurality of blades. For example, a rotorcraft may have at least one lift rotor. Such a rotor can be relatively bulky when the aircraft is on the ground or on board a ship.
Consequently, a blade may include a folding device to enable it to be put into a position that minimizes the overall size of the aircraft. For example, the blades of a lift rotor of a rotorcraft may be folded so as to extend substantially parallel to an antero-posterior plane of symmetry of the aircraft.
A blade may comprise an airfoil and a cuff. The airfoil is fastened to the cuff, the cuff being fastened by hinge and retaining means to a hub of the rotor.
In an embodiment, the airfoil has two bushings arranged vertically. Each bushing thus presents a vertical direction of symmetry that extends in the thickness direction of the airfoil, being substantially perpendicular to the suction side and pressure side faces of the airfoil.
Each bushing thus passes through a spar of the airfoil along a vertical direction. For example, the spar may include tapes wound around each bushing. The tapes may be made of composite materials, for example.
Furthermore, the cuff has a clevis provided with two horizontal lugs arranged in elevation one above and the other below the airfoil. Each lug is then provided with one orifice per bushing in the airfoil in order to pass connection pins.
Consequently, the airfoil is fastened to the cuff by two connection pins, each connection pin passing through the clevis of the cuff and a bushing in the airfoil.
In order to fold the blade, an operator can then remove one of the connection pins so as to be able to pivot the airfoil relative to the cuff about the direction of rotation passing along the connection pin that remains in position.
That architecture is advantageous and effective. Nevertheless, it can be understood that the cuff presents thickness that is not negligible in order to enable the clevis to be arranged in elevation above and below the airfoil. The resulting assembly thus presents aerodynamic drag that can degrade the performance of the rotor fitted with the blade.
Arranging a clevis around an airfoil leads to a frontal area being obtained that is of considerable height in a plane perpendicular to a plane of rotation of a rotor. Consequently, this frontal area tends to generate a large amount of aerodynamic drag, giving rise to a loss of power from the rotor and to an increase in fuel consumption by the power plant driving the rotor in rotation in order to overcome a degradation in the performance of the rotor.
Document FR 2 742 726 describes a hinged cuff for connecting an airfoil to a hub. Thus, the cuff has a folding fitting pivotally mounted on a link member. The folding fitting is then fastened by two pins to the airfoil, the link member being fastened to a hub by hinge and retaining means.
Document FR 2 754 779 describes a method of folding by pivoting an airfoil about a pin connecting it to a cuff.
Document U.S. Pat. No. 3,923,422 describes an airfoil having a spar including tapes arranged flat. The tapes are nevertheless twisted at the root of the airfoil so as to be wound around two vertical bushings. Such twisting through about ninety degrees presents the drawback of possibly being destructive, insofar as a spar is constituted mainly by unidirectional fibers when blades are made of composite materials.
Document FR 2 918 347 describes an airfoil having a spar distributed over a leading edge, together with a suction side face and a pressure side face of the blade. A fastener fitting is attached to the root of the airfoil.
That fastener fitting possesses a horizontal shaft perpendicular to the span of the airfoil and to a direction of rotation of the rotor, tapes of the spar being wound in part around that horizontal shaft. In addition, the fastener fitting has vertical orifices passing vertically through the horizontal stud between two tapes of the spar.
Also known are Documents EP 2 540 620 and U.S. Pat. No. 4,738,592.